The phenology of Arctic Ocean surface warming

Abstract

In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near‐term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season.

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

“…The timing of seasonal sea ice melt plays a large role in the total energy absorbed at the surface [151]. More energy can be absorbed, stored, and later released by the ocean if the timing coincides with the midsummer maximum surface net flux [151,152]. Less sea ice is also expected to increase the size and strength of Arctic synoptic variability affecting the proportion of SH and LH fluxes that occur episodically [153].…”

“…For example, during SHEBA the presence of clouds modified the net surface radiative flux by~40 W m −2 [101,103,123,214]. Clouds also directly affect the amount of summertime solar radiation available to melt sea ice and heat the ocean affecting surface turbulent fluxes and sea ice freeze onset in the following autumn and winter [38,152,219]. Depending on the effects of the cloud-modified surface radiative fluxes on the surface temperature, clouds may impact surface turbulent fluxes.…”

“…The ocean mixed-layer depth-the depth communicating with the atmosphere-varies seasonally due to changes in the atmospheric circulation, sea ice, surface radiative fluxes, and SH and LH fluxes storing summer-time energy and releasing it in autumn [152,231,232]. For example, consider the different ocean warming responses to two recent Arctic ice-loss events with different surface conditions in 2007 (ice loss concentrated in Chukchi Sea) and 2012 (ice loss concentrated in the higher-latitude Eastern Beaufort Sea).…”

“…In 2007, sea ice melted at a lower latitude and earlier in the season, hence the exposed ocean experienced a greater net surface radiative flux. In 2012, sea ice loss occurred later in the season and at higher latitudes; the exposed ocean saw a smaller net surface radiative flux for a shorter time and warmed less [152]. Seasonality of ocean temperatures is also influenced by the Pacific Decadal Oscillation (PDO) and the co-location of Arctic storm tracks and sea ice cover [39,178,233,234].…”

“…A range of atmospheric and oceanic forcing mechanisms, including both high and low frequency variability, influence surface turbulent fluxes: atmospheric variability, sea ice extent variability, ocean heat storage, and mixed layer processes [39,104,152,231,246]. This section describes the magnitude of typical surface turbulent flux inter-annual variability, outlines the general factors, and highlights the importance of the episodic nature of air-sea energy exchange.…”